Introduce debug events for Microtask queue.

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index f5a19d116e67eded144057427b2773f180c65480..25be4957153ebf0d7ca977670ae5dede6f9c96d1 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -366,6 +366,7 @@ class Debug {
   void OnBeforeCompile(Handle<Script> script);
   void OnAfterCompile(Handle<Script> script);
   void OnPromiseEvent(Handle<JSObject> data);
+  void OnAsyncTaskEvent(Handle<JSObject> data);
 
   // API facing.
   void SetEventListener(Handle<Object> callback, Handle<Object> data);
@@ -538,6 +539,8 @@ class Debug {
       Handle<Script> script, v8::DebugEvent type);
   MUST_USE_RESULT MaybeHandle<Object> MakePromiseEvent(
       Handle<JSObject> promise_event);
+  MUST_USE_RESULT MaybeHandle<Object> MakeAsyncTaskEvent(
+      Handle<JSObject> task_event);
 
   // Mirror cache handling.
   void ClearMirrorCache();